1. Field of the Invention
The present invention relates generally to packaged electronic systems and, more specifically to such a system that includes an absorbing cover which reduces the electromagnetic resonance produced by the circuitry of the packaged microwave components.
2. Description of the Prior Art
The circuitry contained in packaged electronic systems is a source of electromagnetic resonance that may adversely affect the performance of the active circuitry contained therein by generating electromagnetic interference (EMI) or radio frequency interference (RFI).
Traditional microwave packages are metal, with a cover grounded to a housing or base. The package covers typically comprise many channels and cavities and, by attaching the package cover to the package base, the closed cavities or channels of the cover provide structural isolation of the electronic fields produced by a particular circuit housed within the package. It is generally known that there can be electromagnetic resonance within these cavities and channels, especially if the circuits are operating at very high frequencies. A number of techniques are described in the prior art that attempt to reduce the resonance effect on the circuitry contained within a microwave package.
As illustrated in FIGS. 1a and 1b, the prior art discloses a technique where electromagnetic interference is reduced by producing a sheet of absorber material (i.e. iron-loaded or ferrite material) and manually adhering the absorber material 11 to the ceiling of the cavities 13 contained on the underside 15 of the package cover 17. Although this technique has produced desirable results in the reduction of electromagnetic interference, the technique requires precise shaping and placement of the absorber material resulting in a complex and manually labor intensive fabrication process.
The technique disclosed in U.S. Pat. No. 5,397,854 attempts to minimize the complexity of the fabrication steps required by the method disclosed above. The ""854 patent describes using an ink which contains a combination of a resin and a microwave absorbing material, such as iron or ferrite and screen printing or mask printing the ink onto the ceilings of the cavities and channels of the package cover. Although the ""854 patent eliminates having to manually align and adhere the sheets of absorber in the cavities and channels of the cover, the method disclosed in the ""854 patent introduces a different set of complexities. For example, a mask or a screen is required where the pattern of the mask or screen must precisely match the pattern of cavities and channels of the cover, the mask or screen must be accurately aligned with the cover prior to the printing process and following the printing process the ink must be hardened through a curing or drying process.
As previously discussed, present packaged electronic systems use a variety of techniques to reduce the electromagnetic interference caused by the emissions of active circuitry. However, these techniques require complicated fabrication processes, and are not cost effective. The greater the complexity, the more assembly costs are increased and reliability decreased.
Based on techniques known in the art for packaged microwave systems, a method for reducing electromagnetic interference of packaged microwave systems while reducing the cost of manufacturing electromagnetic wave absorbing covers is highly desirable.
It is an aspect of the present invention to provide a packaged electronic system that includes a base having a surface and a plurality of discrete electronic components disposed on the base surface. The present invention also includes a cover disposed on the base surface, wherein the cover has a molded body, an exterior surface, and an interior surface. The cover body may be selectively plated and is formed of a material having electromagnetic wave-absorbing characteristics.